It is known that high-molecular weight thermoplastic polymers have been used as matrix resins and may be modified (e.g. to improve and/or impart desired physical properties to the polymers) by incorporating other additive materials thereinto. Representative examples of additive materials that have been incorporated into thermoplastic matrix resin include non-thermoplastic fillers (e.g., so as to reinforce the polymer) and thermoplastic additive resins (e.g., so as to modify the heat resistance, impact resistance, chemical resistance and/or surface gloss characteristics of the matrix resin). Furthermore, attempts have been made in the past to enhance the blending efficiency and/or homogeneity of resulting melt-blended resin compositions. For example, various techniques such as compatibilization, dynamic vulcanization and reaction extrusion have been proposed with a view towards enhancing the manner in which resin components may be blended with one another so as to achieve desired property modifications.
In order to obtain desired effects, thermoplastic additive resins have typically been incorporated into matrix resins in relatively large amounts so as to improve thermal and mechanical properties. However, using thermoplastic additive resins in such large amounts inevitably affects other desired physical properties adversely. Attempts have therefore been made to improve the mechanical properties of matrix resin through formation of an interpenetrating three-dimensional network structure using lesser amounts of additive resin. However, in order to form a three-dimensional network, it has typically been necessary to employ specialized and relatively complex processing techniques. For example, three-dimensional networks of an additive resin in a matrix resin have been formed by simultaneously polymerizing the matrix resin monomer and the additive resin monomer. Similarly, preliminary polymerization of one of the matrix or additive resin monomers to a desired extent followed by polymerization of both monomer components or chemical reaction utilizing a functional group have been employed.
There is therefore no known post-polymerization technique in the art for forming a thermoplastic interpenetrating three-dimensional network structure using small amounts of the additive resin. It is towards achieving such a technique that the present invention is directed.
Broadly, the present invention is directed to forming filled resin compositions having a first continuous phase comprised of a thermoplastic matrix resin, and a second continuous phase comprised of (a) a thermoplastic additive resin dispersed homogeneously throughout the matrix resin in the form of an interconnected three-dimensional network, and (b) a filler material homogeneously dispersed through the interconnected three-dimensional network. As a result of the interpenetrating three-dimensional network that is formed, the thermoplastic additive and filler may be employed in lesser quantities as compared to melt-blended filled thermoplastic compositions of the prior art while achieving comparable (and usually improved) property enhancements. Thus, the problems typically associated with incorporating relatively large amounts of additive resin within a matrix resin as described briefly above have been minimized (if not alleviated) according to the present invention.
The present invention more specifically relates to forming a melt-blended filled thermoplastic resin composition by selecting the thermoplastic matrix resin and the filler material such that one exhibits a higher surface tension during melt blending as compared to the other. On the other hand, the thermoplastic additive is selected such that it exhibits a surface tension during melt-blending that is an intermediate value between the higher and lower surface tension values of the thermoplastic matrix resin and the filler. In other words, the surface tension values .delta..sub.1, .delta..sub.2, .delta..sub.3 during melt-blending of the thermoplastic matrix resin, the filler material, and the thermoplastic additive, respectively, are each selected so as to satisfy the relationships: EQU .delta..sub.1 &lt;.delta..sub.3 &lt;.delta..sub.2 ;
or EQU .delta..sub.1 &lt;.delta..sub.3 &lt;.delta..sub.2.
Further aspects and advantages of the invention will become more clear after careful consideration is given to the following detailed description thereof.